I am encountering the same issue with uploading as well and it seems to have been since updating the EE to 2.5.3 that caused the issue to break uploading at all. I’ve applied some of the custom patches that have been suggested in the Bug Report but still have the same issue where the upload does not work. It isn’t a fault it seems of the extensions but something more with the updates in the new EE version that are the cause. I’m running EE 2.5.3 with Zoo Visitor, S3 Simple Uploader and Matrix (all up to date).
The issue was raised with Pixel and Tonic here:
But process of elimination, it seems like the EE 2.5.3 broke down what was previously functioning normally. Made the mistake of doing this on a live site, so I’m getting plenty of flack until it gets fixed.
Also, I’ve split the page in to two so that updating images is separate to updating profile text data, it’s only the images that have the issue and not the text field based form.